Many scientific problems in building physics can be described by PDEs. There are a lot of software programs available in which one specific PDE is solved. They are developed in order to get the simulation results in a short time and are most often emphasized on the simplicity of input of data, e.g. geometrical data. A disadvantage is that they often are not very flexible when the user wants to change or combine models. Also they most often act as black boxes. The commercially available software package FemLab is evaluated as solver for building physics problems based on partial differential equations (PDEs). The software is designed to simulate systems of coupled PDEs, 1D, 2D or 3D, non-linear and time dependent. An important feature of FemLab is that the user can focus on the model (PDE coefficients on the domain and boundary) and does not have to spend much time on solving and visualization. In this paper, 4 cases are considered. First, in order to illustrate how FemLab works, an example including the complete code for solving as well as the results are given for a simple 2D steady state heat transfer problem. In the next 2 cases, the reliability is tested for two very different building physics problems: A 2D dynamic airflow problem, modeled using Navier Stokes and buoyancy (Sinha, 2000), and a 1D dynamic non-linear moisture transport in a porous material (Brocken 1998). These simulation results are validated and show a good agreement with measurements. In the last case, FemLab's capability of simulating 3D problems is shown by a dynamic combined heat and moisture transport problem. This example is a 3D extension of a given 2D problem from IEA Annex 24 (Kunzel, 1996). For all models the crucial parts of the codes (geometry, PDEs and boundary specifications) are given.

• CFD - computational fluid dynamics

1. Modeling and solving building physics problems with FemLab